Synchronizing circuits



Aug. 28, 1951 R. c. WEBB sYNcHRoNIzING CIRCUITS Filed Deo. 3l. 1949 Vl'lll RCPW@ Patented ug. 28, ,1951

UNITED STATES PATENT oFFicE vSYNCIIR*Oll,Ns CIRCUITS Richard Radio Delaware Application December 3 2 Claims.

The present invention relates to electronic synchronizing circuits and in more particularity, although not necessarily exclusively, to synchronizing circuits for time constant type electronic oscillators.

In even still more particularity, the present invention relates to frequency stabilizing circuits for television synchronizing generators in which there is employed a time constant type master oscillator designated for stabilization in accordance with local public utilities 60 cycle power line voltage.

In the electronic art to which the present invention pertains, there commonly arises the need for synchronizing or stabilizing the operating frequency of time constant type oscillators, for eX- ample, multivibrator r relaxation type time bases and the like. Perhaps the most common form of such circuit control is found in present-day .television receivers in which automatic frequency control of the horizontal deflection circuit is accomplished by frequency comparison between received horizontal sync and the operating frequency of the horizontal deflection circuit multivibrator or relaxation oscillator.

A still further application of automatic frequency control of time constant type oscillators may be found in television synchronizing signal generators wherein it is desirable to lock-in the' synchronizing signal generator with the local public utilities power line frequency. In such sync generator control circuits, 1t has been the practice to compare the frequency of the vertical sync pulse or vertical blanking pulse developed by the sync generator with the 60 cycle sinusoidal voltage of the power line terminals to the sync generator apparatus. The comparison circuit may take a variety of forms but most generally comprises a bridge-rectifier type of comparator circuit well known in the art and described, for example, in 1943 issue of The Proceedings of the I. R. E. in an article entitled Automatic Frequency and Phase Control of Synchronization in Television Receivers by Wendt and Fredendall. The output voltage of such a bridge-rectier type comparator circuit isf'unidirectional in nature and is generally applied to the control electrode of one of the electron discharge tubes of the time constant master oscillator.

Accordingly, automatic frequency control of the operating frequency of time constant type oscillators such as blocking oscillators, multivibrators, etc. by controlling the bias conditions of associated electron discharge tubes in accordance lwith C. Webb, Princeton, Corporation of America,

N. J., assignor to a corporation of 1, 1949, Serial No. 136,187

(Cl. Z50- 36) control voltages developed by frequency comparator circuits is well known. However, depending upon the electrical characteristics of the discharge tubes involved in such time constant oscillator circuits, the degree, stability and linearity of frequency control may be found wanting in many instances. Moreover, it is frequently found that in controlling the frequency of a time constant type oscillator by means of controlling disbias, undesirable variations in the developed signal amplitude result.

It is therefore a purpose of the present invention to provide an improved type of synchronizing or automatic frequency control circuit for time constant type oscillators.

It is another purpose of the present invention to provide an improved type of automatic frequency control for time constant type oscillators of a type in which it is undesirable to exercise grid bias control of associated discharge tubes.

A still further object of the present invention resides in the provision of an improved frequency control circuit for time constant type oscillators of the multivibrator or relaxation type whereby a more versatile and smoother acting control characteristic is obtained.

Another object of the present invention resides in the provision of an improved vform of automatic frequency control for television synchronizing signal generators of the type employing a time constant form of multivibrator.

It is yet another object of the present invention to provide a frequency control time constant multivibrator circuit in which the amplitude of developed signal is rendered substantially independent vof the influence of frequency control action.

- In the application of the present frequency control system to time constant type oscillators the present invention contemplates the use of an electron discharge tube whose anode-cathode path is `directly associated with one or more of the time constant circuits upon which the oscillator depends for frequency definition. The electron discharge tube is connected such that as the resistance of its anode-cathode path is varied in accordance with voltage variations applied to its associated control electrode, the RC value of the time constant 4circuit with which it is connected is altered so as to effect a change in the operating frequency of the time constant oscillator.

For automatic frequency control of such time constant oscillators embodying the present invention, the voltage applied to the control electrode of the variable resistance discharge tube may be derived from a frequency comparator cirfrequency l accesos cuit which co pares the signal frequency of the in the art and is described in U. S. Patent Nd. time constant oscillator with some standard fre- 2,383,822 entitled Oscillation Generator by Kurt quency source. Schlesinger, issued August 28, 1945. As indi- A more complete understanding of the charcated, the envelope 38 comprises two discharge acter and operational mode of the present in- 6 tube sections 40 and 42, the input and output cirvention, as Well as many other of its objects and cuits of the two tubes being respectively coupled trol of a television synchronizing;signalrgenerator., causingV theI c athodes of both discharge tubes to Referring now to the drawing, there. isilluse. wy swing` negatively. As thea7 Swing negatively, the trated in the dotted line area l0 a typical form of control electrode 54T of discharge tube 42 begins to time constant type oscillator which. is shown Condllet and acts to discharge the caDaCOr 50 in nal generator. Further, by way of example, the 20 electrode 54 is normally established so that the master oscillator has been assigned anominal freanode Current 111 the tube Se0151011 42 decreases quency of 31 500 cycles per second in order to The resulting increased conduction of tube secform the basis of standard television synchroniztion 4i! Causes the 00111111011 CahOdeS t0 become ing signal formation In accordance with conmore positive and re-establish conditions for the veritional practice, the pulse output app@aringfai;y4 2li uninhibited linear charge of the capacitor. 5,0. It..

controlsignal for control of the horizontal wave.- 30.y through Which it. charges from the source of BV form processing circuits Hi.- At the` outputchan- DOWer supply potential 56.

nels-2U, 22.*,and 2 4of'thewaveform processing cir- According to the present invention, the value of.v cuitsthereare, respectively, indicated horizontal the time constant circuit includingvCapacitor: 501s formation and horizontaldrive pulse information. 9.5Y anode-cathode circuit is, via, resistance 60, con-- tor l01S, ri further accord kvvi-th conventionaly synportion of the charging` resistance 5-2. Additionall chronizing signal. generator. practice. applied to capacitors 62 and 64. are connectedoneither side.

theinputof a verticalffrequency divider 2,6.Which of. the seriesfresistance 60 to ground for filtering,J establishes a 525:1 divisionofl the.y master oscilla.-v 4Q purposes. Thus, ift e discharge tube 58 is made,

quency: divider-'stages iiicascade; therproductyof 45 On the other hand,l if the discharge tube '.58v is.

theutpui; terminal- 28; Accordingly, these-'con'- 5,0n capacitor freniains constant and-the bias ap.-

trol signals are appliedtovthe waveform p rocessplied to the control electrode 48 of tube seclng circuits 3i)l atwhose outputs 32, 3 4 and-.36 tion 4U remains constant, it is evident that the are respectively found verticall sync pulse mforamplitude of the sawtooth developed across the mation, verticallo1anl ;ing.informationTandV verti-4 capacitor 5 Jv will remain substantially constant.. -cal drive information. 55, regardless of the time constant value This of Inasmuch as theiactualforins` of modernday course, means that the C011101 D11-15e |211- der horizontal and` vertical frequency divider circuits du Vertical frequency dividers i4 and 2 I4 and 26 as well as the Waveform processingkv Another way of viewing thenovel action of the circuits i8 ande'l is thought for present pur-f present invention is to consider the discharge p os esto besuperfluous If, however, further in. tube 58 not only as a device for controlling the formation as to the circuit coniguration suitcomposite time constant of the circuit associated.

able for application in these. block represeiita.-V 65` with capacitor 50 but, also as a means for Vary tions is.v desired, reference.. maybe made. to .an vingythev` charging potential `available to ther-time@I article entitled A,Precision lTelevision Synchro. constant circuit,comprisingl capacitor;50.andqre-4 nizingSignal Generatori by J..P..Sniith= and AldaQ. sistorVv 52. Byiwayfoflexample, the terniinall;4

:, iszsslto '.r. P. smith entitiedfsystem,formo! ingpotentiai forthe. capacitor teso tnatasl'ti Iiicing Electrical Impulses. issued October. 1 1.. conductance,r ofthedischarge tube 58qinoreases, 948.

f'lh'eparticular form. ofmasterbscillatorsshowm pacitory 5i)r willffbe -reduced. and, theifrequency of... ;i;the.dotted. line area. |0.is furtherwell. known up oscillation.will.decrease.I Ori-f. the other.y handy@ 5. should the conductance of the discharge tube 58 decrease, the 1R drop through resistance 54 will decrease and the potential at terminal 9 will increase. This, in turn, allows capacitor 56 to more quickly charge up, through resistance 52, to a predetermined recycling level and thereby increase the oscillator frequency. It is noted that the potentiometer 4l may be used to adjust the nominal operating frequency of the master oscillator operation since it, in effect, determines the amplitude to which the capacitor 50 must charge in order to initiate recycling of the multivibrator circuit.

Any means may be used to vary the conductance of the discharge path 58. In the example shown the control electrode 66 of the discharge tube 58 is adapted for control from the output of a bridge-rectier type of frequency comparator circuit comprising diodes 68 and 10, as well as resistance elements 12, 14, 16, 18, 80 and 82, all taken in connection with capacitive elements 84 and 86. This form of frequency comparator circuit is well known in the art and its general operating mode is fully described in the above-referenced article by Wendt and Fredendall appearing in the January, 1943 issue of The Proceedings of the I. R. E. As indicated, push-pull vertical blanking signals are applied across one arm of the bridge by means of the discharge tube 90, the signals at its anode and cathode, in the connection shown, being 180 degrees out of phase with one another. Local 60 cycle power line frequency is then applied through resistance 82 to the center of the bridge circuit by means of the transformer 92. Thus, the unilateral potential appearing at the junction 94 of the diodes 68 and 10 will vary in accordance with the frequency and phase difference between the 60 cycle power line and the vertical blanking signal developed by the synchronizing generator. Accordingly, with the electrical sense of the developed signal being established as shown in the drawing, this unilateral control potential developed at the output terminal 94 of the bridge comparator circuit may be filtered by means of the elements 96, 98; |00, |04 and |06 for stabilizing control of the master oscillator frequency via the above-described discharge tube 58. Thus, the master oscillator frequency will be automatically adjusted by means of the discharge tube 58 so that isochronism may be obtained between the 60 cycle power line and the vertical blanking pulse.

It is evident that although the present invention has been shown in connection with a time constant oscillator used as a master oscillator for a television synchronizing signal generator that its utility is in no way limited thereto. For eX- ample, the novel control system of the present invention may be well applied to other forms of time constant oscillators such as the conventional blocking oscillator found in the horizontal deflection circuits of present-day television receivers. In such latter use, if automatic frequency control were desired, the frequency comparator circuit would be adapted to compare incoming horizontal sync as received by the receiver, with the signal frequency developed by the blocking oscillator.

From the foregoing, it may be seen that the present invention provides a substantial improvement in time constant type oscillator frequency control, and it is eminently adapted for automatic frequency control applications in which the time constant oscillator with which it is associated is to be frequency stabilized from a standardizing frequency source.

lHaving thus described my invention, what I claim is:

1. In a frequency stabilized sawtooth generating system includinga source of standardizing frequency, the combination of, an electron discharge device including a cathode, an anode and a control electrode, an electrical storage element connected between the control electrode and a predetermined point of fixed potential, means for supplying charging energy at a substantially uniform rate in a positive direction to the storage element, means to bias the cathode of the discharge device relative to the`point of fixed potential to a predetermined amount, a second electron discharge device also including a cathode, a control electrode and an anode, an impedance element connected between the anode of the first electron discharge device and said point of fixed potential, a connection between the second named control electrode and an intermediate point of said impedance element, a connection between the cathode of the second discharge device and the cathode of the first discharge device, so that at a time period when the charge acquired by the storage element is equal to the cathode bias, a discharge of the storage element is initiated and the cathode approaches at the potential of the fixed point so as to accelerate the discharge rate of the storage element, a third electron discharge tube having an anode-cathode path and a control electrode, connections placing the anodecathode path of said third discharge tube in shunt with said storage element, a frequency comparator circuit connected to receive and compare both said standardizing frequency and signals derived from the output of said sawtooth generating system to develop a control potential representative of frequency differences between the compared signals, and connections applying said control potential to said third electron discharge tube control electrode.

2. Apparatus according to claim l wherein there is additionally provided a low pass filter circuit connected in series with the connection of said third discharge tube anode and said first discharge tube control electrode.

RICHARD C. WEBB.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,201,978 Bedford May 28, 1940 2,383,822 Schlesinger Aug. 26, 1945 2,389,025 Campbell Nov. 13, 1945 2,477,076 Miller July 26, 1949 2,492,018 Sunstein Dec. 20, 1949 2,521,058 Goldberg Sept. 5, 1950 

